The present invention relates generally to metal oxide films, and more particularly to metal oxide films formed from metal salts and water soluble polymers. These films may be used in many applications, one example of which is in fuel cells.
Fuel cells use an electrochemical energy conversion of fuel (including but not limited to hydrogen, propane, methane, carbon monoxide, and the like) and oxidant(s) into electricity and heat. It is anticipated that fuel cells may be able to replace primary and secondary batteries as a portable power supply. In fuel cells, the fuel (usually containing a source of hydrogen) is oxidized typically with a source of oxygen to produce (primarily) water and carbon dioxide. The oxidation reaction at the anode, which liberates electrons, in combination with the reduction reaction at the cathode, which consumes electrons, results in a useful electrical voltage and current through the load.
As such, fuel cells provide a direct current (DC) voltage that may be used to power motors, lights, electrical appliances, etc. A solid oxide fuel cell (SOFC) is one type of fuel cell that may be useful in portable or non-portable applications.
The material properties which are generally desirable in order to obtain high performing fuel cell devices, also make fabrication of those fuel cell devices a significant challenge.
SOFC's often contain electrolytes and electrodes made from metal oxide films. Deposition of thin metal oxide films has been accomplished with many methods, including atomic layer deposition (ALD), Physical Vapor Deposition (PVD), Chemical Vapor Deposition (CVD), Plasma Enhanced Chemical Vapor Deposition (PECVD), Molecular Beam Epitaxy (MBE), Metal Organic Chemical Vapor Deposition (MOCVD), sputtering, evaporation, and various wet chemical methods. The wet chemical methods offer the advantages of low cost equipment and high throughput. However, some examples of deposition methods and drawbacks associated therewith include the following.
Sol-gel is one of the most common wet deposition methods, but suffers from high material cost and very sensitive process conditions, including a controlled atmosphere. Sol-gel reagents are generally used in carefully controlled regimes of pH and temperature. Additionally, there is generally a narrow process window to produce a coherent film.
A metal-organic deposition (MOD) method is another wet method. MOD generally requires inexpensive materials, but has poor wetting characteristics due in part to the glycols used. Further, the MOD process generally requires a time-consuming chelation process.
MBE and ALD methods generally involve expensive equipment and materials. CVD, PECVD, and MOCVD generally use costly equipment and volatile precursors that may not be readily available. Sputtering and evaporation deposition techniques generally require expensive equipment and stoichiometries which may in some instances be difficult to control.